ONLY 100mm Celotex !? (Over slab insulation, then UFH and 75mm sand/cement screed)

[PaulD]

Ok so I posted this same question a while ago on another forum and all I got in reply was "why ONLY 100mm ?"

 

I've got 30m x 15m barn, so 90m perimeter and 450sqm

 

Due to final floor level, I have 100mm for insulation to play with, and was originally thinking Celotex GA4100 with u-value of 0,22 

 

Depending on supplier, cost of 150 sheets is circa £35 each so £5250

 

But then I got thinking, if 100mm really isn't enough maybe I should go for a better product, like Ecotherm Eco-versal with a u-value of 0.13 but the cost rises to £37 each so £5550

 

Any thoughts on Ecotherm ? Seems a no brainer for the minimal extra cost ? 

 

Is there a another better option ? I guess it comes down to cost vs lifetime savings on energy which is probably a very complicated calculation.

 

Is it worth going for a better product around the perimeter ? since this is where more heat is lost ?

 

Can anyone shed any light or offer any advice, this is beginning to give me a headache !!

 

Thanks in advance !

[Redbeard]

From Eco Therm's website: "Eco-Versal is a 5 in 1 insulation board with a thermal conductivity of 0.022 W/mK. "

 

The relevant values are the thermal conductivity (Lambda) values. In both cases they are 0.022, so the Eco Therm product will give you the same result. Yes, 100mm Celotex will give you a (not very exciting) U value of 0.22 for the insulation only, but so will the Eco Therm. This figure does not take into account the perimeter/area calc, but the 0.13 U value does. So Celotex will give you 0.13 and Eco Therm will too, using the same calc. Therefore the minimal extra cost will be a minimal extra cost for exactly the same result.

[Jenki]

Is this under building control?.

In Scotland none of those at that thickness  would pass current building regulations, not sure what England's regs are now.

[Jenki]

Could you look at a liquid screed at 50mm and boost the insulation🤔

[PaulD]

17 minutes ago, Redbeard said:

From Eco Therm's website: "Eco-Versal is a 5 in 1 insulation board with a thermal conductivity of 0.022 W/mK. "

 

The relevant values are the thermal conductivity (Lambda) values. In both cases they are 0.022, so the Eco Therm product will give you the same result. Yes, 100mm Celotex will give you a (not very exciting) U value of 0.22 for the insulation only, but so will the Eco Therm. This figure does not take into account the perimeter/area calc, but the 0.13 U value does. So Celotex will give you 0.13 and Eco Therm will too, using the same calc. Therefore the minimal extra cost will be a minimal extra cost for exactly the same result.

 

Thanks Redbeard, it seems I've cocked up my figures, so I guess the question is, is there any alternative to 100mm Celotex which offers, say, double the performance but not double the cost ?

 

 

14 minutes ago, Jenki said:

Could you look at a liquid screed at 50mm and boost the insulation🤔

 

Hi Jenki, my builder, plasterer and the guy doing my UFH and screed all agree that sand/cement screed is a far better product than flowscreed - but you're right, that's an option.

[TonyT]

Are you installing UFH?

[saveasteading]

The perimeter to area principle has been dropped from marketing so they can sell more insulation.

At about 25 x 25 you don't technically need any insulation in the floor, tho it is still sensible.

I would be tempted to use 200 round the perimeter (5m wide ish ) and 100 in the middle. Plus good detailing at the outside edge.

 

I would have to think how to present this though.

 

I was very impressed with our liquid screed. 4 hours and done.

[Bonner]

+1 for flow screed. You won’t find anything better than standard PIR, all you can do is increase thickness. No chance of raising the finished floor level?

[Dave Jones]

9 hours ago, PaulD said:

Ok so I posted this same question a while ago on another forum and all I got in reply was "why ONLY 100mm ?"

 

I've got 30m x 15m barn, so 90m perimeter and 450sqm

 

Due to final floor level, I have 100mm for insulation to play with, and was originally thinking Celotex GA4100 with u-value of 0,22 

 

Depending on supplier, cost of 150 sheets is circa £35 each so £5250

 

But then I got thinking, if 100mm really isn't enough maybe I should go for a better product, like Ecotherm Eco-versal with a u-value of 0.13 but the cost rises to £37 each so £5550

 

Any thoughts on Ecotherm ? Seems a no brainer for the minimal extra cost ? 

 

Is there a another better option ? I guess it comes down to cost vs lifetime savings on energy which is probably a very complicated calculation.

 

Is it worth going for a better product around the perimeter ? since this is where more heat is lost ?

 

Can anyone shed any light or offer any advice, this is beginning to give me a headache !!

 

Thanks in advance !

 

better option is 300mm of EPS. half the price of the equivalent celotex and far far superior.

 

the standard mindset from architects/builders/specifiers that only 100mm needs to be allowed for insulation in the build up has to change.

[saveasteading]

12 minutes ago, Dave Jones said:

300mm of EPS. half the price of the equivalent celotex 

Half the price and half the performance.

[Dave Jones]

In order to not mislead.

 

300mm eps > 100mm celotex for BETTER performance.

 

 

[MikeGrahamT21]

Also take a look here, may save you a small fortune: https://www.secondsandco.co.uk/deliveredboards

 

If you get the kooltherm boards, they are a step up from PIR in terms of performance, they're phenolic boards.

[jayc89]

Do away with the screed and have the concrete as your finished floor. Use the space saving for more insulation. 

[saveasteading]

Let's go back a step.

What depth is available for your floor and what surface is there now?

 

[PaulD]

3 hours ago, saveasteading said:

Half the price and half the performance.

 

I have 100mm for insulation, non negotiable ! so I need the best solution given this constraint. Currently have slab down an just need to decide on insulation before booking UFH install.

Edited June 6, 2023 by PaulD
added detail

[saveasteading]

Ok, slab already down is the answer I was needing.

I suggest 2 layers of 50mm PIR of any make. Stagger the joints and butt neatly and there won't be gaps.

Really look hard at the perimeter to see if you can limit horizontal heat loss.

 

If you are struggling to show compliance you can trade off, and put more in walls and roof.

For your chunky floor plan, the insulation effect is better than the straight U value anyway.

 

[Thorfun]

1 hour ago, PaulD said:

 

I have 100mm for insulation, non negotiable ! so I need the best solution given this constraint. Currently have slab down an just need to decide on insulation before booking UFH install.

can you go liquid screed at 50mm? would give you an extra 20mm insulation. we have Cemfloor screed and it's so quick to pour and can work on it within 48hours and tile after 4 days with no laitence to remove.

 

if you're stuck with 100mm then as was mentioned above the Kingspan phenolic insulation will give slightly better performance that normal PIR.

[saveasteading]

13 minutes ago, Thorfun said:

Kingspan phenolic insulation

Depends on cost which I haven't checked, but yes you could upgrade ti this. If it is expensive then I would probably use it as the upper layer and only nearer the perimeter.

Not much heat gets lost to earth when distant from the outside walls, and the insulation nearest the screed has mure effect than the deeper levels.

 

One thing before committing to a thinner screed. How level is the slab? You don't want a nominally 50mm screed that thins to less than that in some areas.  A technically perfect slab can be up and down quite a lot. 

[Andehh]

+1 for a 50/60mm flow screed and adding an extra 25 or 50mm odd to insulation.

[Temp]

Phenolic boards such Kingspan K103 have a better thermal conductivity than PIR but not by much 0.018 vs 0.022 W/mk I think. That's about 18% better.

 

When you screed the floor form expansion joints at doorways. Screed can shrink very slightly and form a crack at doorways. This crack is never straight and can propagate through tiles or stone. The expansion joint forms a deliberate crack that you can cover with a grout line or door sill.